Apparatus for cooling of vacuum-cast ingots

ABSTRACT

An ingot of metal continuously cast under vacuum is withdrawn into a cooling chamber maintained at a pressure intermediate casting pressure and atmospheric pressure and cooled therein by sprays of cooling liquid. The seal between the chambers is that effected between the molten metal in the ingot mold and the mold.

United States Patent 1191 1111 3,800,856

Mizikar et a1. 1 1 Apr. 2, 1974 [54] APPARATUS FOR COOLING 0F 3,310,8503/1967 Armbruster 164 64 VACUUM-CAST INGOTS [75] Inventors: Eugene A.Mizikar, Clairton; FOREIGN PATENTS OR APPLICATIONS Frederick H, Rehmus,Baldwin 725,586 1/1966 Canada 164/89 Borough, both of Pa.

[ Assigneei Jifnes & Lallghlin Steel Corporation, Primary ExaminerJ.Spencer Overholser Plttsburgh, Assistant Examiner-John E. Roethel il M y29 Attorney, Agent, 0! FirmGerald White; A.

[21] App]. No; 364,456 Zalenski Related US. Application Data [60]Division of Ser. No. 156,554, June 24, 1971, Pat. No.

3,759,312, which is a continuation of Ser. No. [57] ABSTRACT 869,816,Oct. 27, 1969, abandoned.

An ingot of metal continuously cast under vacuum is U-S. Cl. withdrawninto a cooling chamber maintained at a [5 pressure intennediate castingpressure and atmo- Fleld of Search 89, 257, 258, spheric pressure andcooled therein by sprays of cool- 164/281, 283 ing liquid. Theseal-between the chambers is that effected between the molten metal inthe ingot mold [56] References Cited and the mold UNITED STATES PATENTS3,099,053 7/1963 Eliot 164/64 4 Claims, 3 Drawing Figures APPARATUS FORCOOLING OF VACUUM-CAST INGOTS This application is a division of ourapplication Ser. No. 156,554 filed June 24, 1971, now U.S. Pat. No.3,759,312, which in turn is a continuation of our application Ser. No.869,816, filed Oct. 27, 1969, now abandoned. This invention relates tothe cooling of vacuumcast ingots and the like. It is more particularlyconcerned with cooling of such bodies by spraying them with coolingliquid under subatmospheric pressure conditions.

Certain grades of metals and alloys, both ferrous and nonferrous aremost advantageously cast or refined and cast under vacuum, so-called.That term generally means subatmospheric pressures on the order of 10'mm of Hg. The ingots so produced are frequently cast into open end moldsand are withdrawn from the bottom of the mold at a controlled rate. Afactor limiting the casting rate of such ingots is their rate ofcooling. The cast ingots must be cooled in the reduced pressure zone inwhich they are cast until no molten metal is exposed to the surroundingatmosphere.

Heretofore, the mold and the apparatus for withdrawing the ingottherefrom has been enclosed in the evacuated chamber in which the ingotis cast. The ingot can cool only by radiation, and it is usuallywithdrawn from the mold in proximity to water cooled elements which actas heat sinks. The cooling rate so obtained is low.

It is commonplace to cool ingots continuously cast at normal atmosphericpressure by sprays of cooling liquid, usually water. The cooling ratesso obtained are high. Heretofore, it has not been considered possible tocool hot ingots by sprays of water or other cooling liquid under thereduced pressures required for vacuum casting. When water is sprayedthrough a nozzle, it expands and loses temperature. It is known thatwhen water is sprayed into a chamber maintained at vacuum castingpressure, it either vaporizes or appears as snow or ice. Its coolingproperties in either of these states are much inferior to thoseproperties in its liquid state.

It is an object of our invention to provide apparatus and process foraccelerated liquid cooling of vacuum cast ingots or the like. It isanother object to provide such apparatus and process for cooling vacuumcast ingots under a pressure intermediate vacuum casting pressure andatmospheric pressure. It is still another object to provide suchapparatus and process for continuously withdrawing a vacuum cast ingotinto a cooling chamber of intermediate pressure and continuously coolingit therein. Additional objects of our invention will appear in thecourse of the following description thereof.

Vacuum cast ingots are conventionally cooled in a vacuum because it isnot feasible to withdraw them continuously from the vacuum chamber. Thedifficulty is in providing a seal between ingot surface and chamber thatwill support a pressure differential between atmospheric pressure andpressures of about 10' mm of Hg. We have discovered that the seal formedbetween the molten metal teemed into the ingot mold and the mold willsupport a significant pressure differential, though not of the orderabove mentioned, and that the ingot can be liquid spray cooled in acooling chamber at a subatmospheric pressure higher than the castingchamber pressure. Our invention will be more readily comprehended byreference to the attached drawings of an embodiment thereof presentlypreferred by us.

FIG. 1 is an elevation, partially schematic and partially incross-section, of apparatus of our invention.

FIG. 2 is an enlarged'detail of. the spray nozzle arrangement of theapparatus of FIG. 1.

FIG. 3 is an enlarged detail in cross-section of the seal between themolten metal and the ingot mold in FIG. 1.

In the figures, chamber 1 adapted for vacuum casting of metals enclosesa tundish 2 which holds molten metal 3 and is replenished from time totime by means not shown. Tundish 2 is provided with a bottom nozzle 4through which the molten metal 3 flows into an open end upright mold 5.Chamber 1 is sealed to the outside of mold 5 by sealing means 6.

Also sealed to the mold 5 by sealing means 6 is a closed cooling chamber7 into which the solidified ingot 8 descends from the lower end of mold5. Below cooling chamber 7 and sealed to the lower end thereof ishydraulic cylinder 9. The piston rod of cylinder 9 is capable ofextension upwardly to the bottom of mold 5 and carries a plug 11 whichat the beginning of the casting operation is positioned inside the lowerend of mold 5. The molten metal 3 teemed into mold 5 falls onto plug 1 land freezes there. As the ingot 8 builds up the piston rod 10 ofhydraulic cylinder 9 is retracted, lowering plug 11 and ingot 8 intocooling chamber 7. The cooling chamber 7 is provided with a door, notshown, through which ingot 8 is removed after it has been cooled.

Out of cooling chamber 7 opens an exhaust duct 13 which is connected tosteam evacuator 14. Steam is supplied to evacuator 14 through steam line15 from a source not shown. Evacuator l4 discharges into a barometriccondenser 16 which is supplied with water through pipe line 17 from asource not shown. The condensate from condenser 16 is discharged throughbarometric leg 18 into a sump 19 provided with a weir 20 arranged tomaintain a liquid level in sump 19 above the lower end of barometric leg18. The overflow of weir 20 is carried off by drain pipe 21.

Within cooling chamber 7 banks of vertically spaced nozzles 23-23 aredisposed on all sides of the path of travel of ingot 8, so as to spraycooling liquid on the hot ingot. The construction of these banks 23 isshown in detail in FIG. 2. Each bank 23 comprises a vertical pipe 25 towhich are attached vertically spaced spray nozzles 2626. Cooling liquidis supplied from a source not shown through pipe 27 which connects witheach vertical pipe 25. The lower end of cooling chamber 7 is formed sothat liquid drains therefrom through a barometric leg 28 into a sump 29.Sump 29, like sump 19 previously described, is provided with a weir 30which maintains the level of the liquid therein above the lower end ofbarometric leg 28. The overflow of weir 30 is carried off by drain 31.

In the absence of an ingot in mold 5, cooling chamber 7 is connected toclosed chamber 1 by that ingot mold. When molten metal 3 is teemed intomold 5, the molten metal 3 forms with ingot mold 5 a seal as isillustrated in detail in FIG. 3, thereby sealing off chamber 1 fromchamber 7. The molten metal 3 makes contact with the inside wall of mold5 near its upper end over an area 33. The molten metal 3 begins tofreeze in a thin skin 34 from the bottom upwards. On freezing, this skin34 tends to shrink away from mold 5, degrading the seal, but the seal isconstantly renewed by fresh molten metal 3 teemed into mold 5 fromtundish 2. The seal, therefore, is that effected by the dynamic head 33of unfrozen metal in ingot mold 5.

We have found that the seal formed between the molten metal being teemedinto the mold and the mold will support a pressure differential on theorder of 5 mm of Hg. By this we mean that the leakage through this sealwill be small enough that it can be accommodated by conventional vacuumpumping apparatus. Those skilled in the art of commercial vacuum castingof metals know that the term seal used with respect to such vacuumsystems is always relative and, in fact, indicates a tolerable rate ofleakage. Such evacuated chambers are always continuously pumped and aseal may comprise or include an actual opening, such as a narrow slit,as long as the leak through it is not large enough to overload thepumping apparatus. For example, in furnaces in which the charge ismelted by electron beams, the electron emitting apparatus is commonlypositioned in a separate chamber maintained at a lower pressure than themelting chamber and the electron beam passes into the melting chamberthrough a slit.

We prefer to cool hot ingots with water sprayed onto the ingot in ourcooling chamber which is maintained by continuous pumping at a pressureon the order of 5 mm Hg. It is most desirable in such circumstances tomaintain the cooling chamber differential pressure so that the absolutecooling chamber present is somewhat greater than about 4.6 mm of Hg.Below a pressure of 4.58 mm of Hg. water sprayed into the coolingchamber either vaporizes or freezes, depending on its temperature, butcannot exist in the liquid state and so is ineffective in cooling theingot. Above a pressure of 4.58 mm Hg., the water exists in the liquidstate over a range of temperatures above C. This range is much narrowerat mm Hg. pressure than it is at atmospheric pressure. However, if thecooling water should freeze as it is sprayed into the chamber, the heatof the ingot will melt it, rather than convert it directly to vapor.Since, as we have mentioned, the pressure in casting chamber 1 is verylow, on the order of mm of Hg., the pressure differential betweencooling chamber 7 and chamber 1 and the absolute pressure in coolingchamber 7 are substantially the same.

It is known that in the liquid cooling at atmospheric pressure of castor hot rolled metal a layer of cooling liquid vapor forms on the surfaceof the metal and tends to insulate the metal from the cooling liquid.This condition is aggravated in our apparatus because the boiling pointof the cooling liquid is lower at the subatmospheric pressure in ourcooling chamber. In order to penetrate this film of vapor the coolingliquid must be sprayed at high pressure from nozzles located close tothe surface of the hot metal. We prefer to use spray pressures of theorder of psi and when casting ingots 6 inches square, for example, toposition the nozzles not more than 4 or 5 inches from the ingot surface.We prefer to supply through the cooling liquid sprays some excess ofcooling liquid over that vaporized so that cooling liquid must bedrained from the cooling chamber through barometric leg 28. The vaporarising from the evaporation of cooling liquid in our cooling chambertends to increase the pressure therein. Therefore, we control theoperation of ejector 14 to maintain a constant differential pressurebetween casting chamber l and cooling chamber 7.

We claim:

1. Apparatus for cooling a metal ingot continuously cast into an openend mold in a casting chamber maintained at a pressure below atmosphericpressure comprising an otherwise closed cooling chamber, means sealingoff the cooling chamber from the casting chamber including the zone ofcontact between molten metal and mold, means for exhausting the coolingchamber so as to maintain therein a pressure intermediate that of thecasting chamber and atmospheric pressure, and spray means positioned inthe cooling chamber adapted and adjusted to spray cooling liquid ontothe surface of the ingot.

2. Apparatus of claim 1 in which the cooling chamber is sealed to themold.

3. Apparatus of claim 1 including means connected to the cooling chamberto drain cooling liquid therefrom arranged as a barometric leg.

4. Apparatus of claim 1 including piston rod means extending into thecooling chamber through a seal in the wall thereof adapted and adjustedto withdraw the ingot from the ingot mold, and means operating thepiston rod positioned outside the cooling chamber.

1. Apparatus for cooling a metal ingot continuously cast into an openend mold in a casting chamber maintained at a pressure below atmosphericpressure comprising an otherwise closed cooling chamber, means sealingoff the cooling chamber from the casting chamber including the zone ofcontact between molten metal and mold, means for exhausting the coolingchamber so as to maintain therein a pressure intermediate that of thecasting chamber and atmospheric pressure, and spray means positioned inthe cooling chamber adapted and adjusted to spRay cooling liquid ontothe surface of the ingot.
 2. Apparatus of claim 1 in which the coolingchamber is sealed to the mold.
 3. Apparatus of claim 1 including meansconnected to the cooling chamber to drain cooling liquid therefromarranged as a barometric leg.
 4. Apparatus of claim 1 including pistonrod means extending into the cooling chamber through a seal in the wallthereof adapted and adjusted to withdraw the ingot from the ingot mold,and means operating the piston rod positioned outside the coolingchamber.